1. Field of the Invention
The present invention relates to an ink-jet ink set, an ink-jet recording method, and an ink-jet recording apparatus.
2. Description of the Related Art
Recording apparatuses employing a so-called ink-jet process, which eject a liquid ink or molten solid ink from a nozzle, slit, porous film, or the like and thereby record images on paper, cloth, film, and the like, have various advantages, such as compactness, lower price, lower noise, and the like. In addition to monochrome printers using black ink which provide favorable printing quality on so-called plain papers including writing paper, copying paper, and the like, recently products that allow full color printing has become commercially available in large numbers, which products have come to occupy a major position in the recording apparatus field. Among these, a so-called piezo ink-jet process that uses a piezoelectric device, and a so-called thermal ink-jet process that uses thermal energy to form ink droplets and thereby record images, have many advantages, including high-speed printing, high-resolution images, and the like.
Inks used in ink-jet recording apparatuses consist mainly of a solvent, a colorant, and an additive. The following properties, among others, are required of the inks: (1) High-resolution, high-density and uniform images are provided without bleeding an ink on a paper; (2) the ink dries quickly on the paper; (3) the images provided have good fastness; and (4) the images provided have good long-term storage stability. In addition, in the case of high-speed high-image-quality ink jet printers for offices that have been placed on the market in recent years, an double side printing capacity is emphasized. An important requirement for these ink-jet printers is to reduce or inhibit the curl and cockle of recording media, which phenomena often occur when plain paper is used.
A possible method for increasing the density of images recorded is to block a process whereby a colorant penetrate into a paper and to cause the colorant to remain on a surface of the paper. For this purpose, in addition to methods of increasing the concentration of colorant in an ink and of increasing the diameter of dispersed colorant particles, a method of using an anion-cation reaction is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2002-79740, and a method of using a coagulation reaction caused by differences in pH between inks is disclosed in JP-A No. 2001-199150. These methods are very effective methods that also have curative properties against feathering and ICB.
In these methods employing a reactive processing solution, high-density images are provided by using an ink and a reactive treatment liquid having a coagulative action, and by coagulating a colorant by bringing the solution into contact with the ink on a paper. However, simultaneous use of an ink and a reactive treatment liquid for printing increases the total amount of liquid ejected onto the paper, causing curl and cockle of the printed paper. Deformation of a recording medium caused by curl and cockle leads to a decrease in image quality due to dislocation of the point of spotting of an ink droplet on the paper and jamming of the paper as it is fed through the printer. In addition, papers thus deformed often come into contact with the print head and damage the nozzle face. The reaction between the two liquids, moreover, which inhibit the penetration and spreading of the ink, decreases the diameter of an ink dot, thereby providing inferior image definition. To counter this phenomenon, it is necessary to print with a high density of ink, which result in an increased quantity the ink ejected, often causing higher incidence of problems such as curl and cockle of recording media and the ink having an inferior drying property due to the increase in the amount of liquid ejected.
A possible method for improving the drying property of an ink is to increase penetration of the ink into paper. This method involves preparing a quick drying by decreasing the surface tension of the ink by adding a penetrant or a surfactant thereto, thereby increasing the permeability of the ink into paper. However, inks with high permeability have the undesirable effect of allowing penetration of colorants into paper, which has disadvantageous result of reducing image density.
To solve the above problems, the following properties are required: (1) Ink droplets spread smoothly after spotting on a paper and provide well defined images; and (2) high-density images are formed even when the total amount of both the ink and the reactive treatment liquid ejected is reduced. If these requirements are satisfied, high density images can be provided while also inhibiting curl and cockle of recording media. Reduction in the amount of the ink and the reactive treatment liquid ejected has many advantages, such as reduced running costs, prolonged life of printer heads, and reduced work load of a maintenance unit and, having a significant positive effect on the performance of an entire system. However, there is currently no technology available that satisfies these requirements.